Voldemort would likely gain more power more quickly. With Harry out of the way, there is no one to oppose him directly in the prophecy sense. The Ministry of Magic would probably fall under his control even faster. The remaining resistance would be much weaker. Families would be afraid to send their children to Hogwarts. Enrollment might drop, and the whole wizarding education system could be in jeopardy. The magical creatures might also sense the shift in power and become more unruly as the balance in the wizarding world is disrupted.
The wizarding world would be in chaos. They would realize too late that they had pinned all their hopes on Harry and neglected him. There would be a great sense of guilt and despair. The Hogwarts students would be shocked and many would feel a deep sense of loss. The teachers might question their own actions and inactions that led to this. The Order of the Phoenix would be in disarray, having lost their main weapon against Voldemort.
Well, Umbridge is not one to tolerate things that go against her idea of order. If she reads fanfic, she could potentially use it as a means to further her control in the fanfic - created wizarding world. For instance, she might see a fanfic that portrays Hogwarts in a different way than she likes and then try to change it back to what she thinks is right. This could lead to a lot of conflict between her and the fanfic creators, as well as the characters within the fanfics who might oppose her actions.
Her death would likely cause a great shockwave throughout the wizarding world. As a member of the Potter family, she represents a symbol of hope and the future. Her death could lead to a sense of despair among many wizards and witches who saw her as a continuation of the Potter legacy. It might also inspire some to take up the fight against any remaining dark forces more vigorously, in her memory.
It would cause great shock. Harry was seen as a symbol of hope even before he started at Hogwarts. His death could lead to increased fear among the wizarding community as they might think Voldemort or other dark forces are getting stronger. It could also lead to a decline in the morale of those fighting against the dark side.
Another idea is that there is a powerful dark wizard other than Voldemort at Hogwarts. This wizard has been hiding in plain sight all along. In Harry's fourth year, he decides to make his move. He uses a powerful dark spell during one of the Triwizard events. Harry, being in the wrong place at the wrong time, is directly affected by the spell and dies instantly, without anyone really knowing who was behind it at first.
If Harry Potter found the Necronomicon in fanfiction, it could have a huge impact on the wizarding world. It might open up new areas of magic study that were previously unthinkable. But it also poses a great threat. Dark wizards could be attracted to the power it represents and start causing trouble. The Ministry of Magic would likely get involved, either to protect Harry or to confiscate the book.
The Auror department would likely be in chaos. There would be a lot of self - reflection and blame - sharing. Some might question the safety protocols of their missions. His death could also lead to a decrease in morale among the younger Aurors who looked up to him. In the wider wizarding world, there would be fear as Harry was seen as a great protector. People might start to worry more about their safety.
The wizarding world would be in chaos. Voldemort might not be as threatened as he was with Harry around. The prophecy about Harry being the one to defeat Voldemort would be nullified, and the dark forces could gain more power. Hogwarts itself might lose some of its hope and protection as Harry was seen as a symbol of the future in the fight against the dark arts.
Well, it might have a huge impact. It could make brooms more accessible and affordable, changing how wizards travel. It could also draw attention from rivals, causing all sorts of magical business drama.
Their relationship could have a significant impact. If they are close, they could present a united front against the dark forces. Their combined influence could sway public opinion towards a more united and positive stance in the wizarding world. For instance, their family name might carry more weight and inspire others to be brave and kind.